There has been a remarkable increase in the demand for portable telephones in metropolitan areas. However, analog systems are increasingly unable to cover the increase in the number of portable telephone subscribers. Accordingly, to address this increase, operation of a commercial digital cellular telephone system in the United States began in 1993 in the form of a time-division multiple access ("TDMA") system. That TDMA digital cellular telephone system implements digital voice (dual-mode) based on the IS-54B standard promulgated by the Telecommunications Industry Association ("TIA") which specifies an analog control channel for control signals, and digital traffic channels for voice and data signals. That dual-mode digital system based on the IS-54B standard analogically controls outgoing and incoming calls and digitally carries the voice and data signals. The communication capacity of the IS-54B TDMA cellular telephone system is limited by the capacity of the analog control channel.
Because the analog control channel of the IS-54B TDMA system limits its communications capacity, a completely digital system (e.g., with a digital control channel) has been developed to more efficiently utilize frequencies. In 1994, the TIA standardized the completely digital TDMA system having a digital control channel and one or more digital traffic channels. The completely digital TDMA system is referred to as the IS-136 standard. Digitizing the control channel in the TDMA system according to the IS-136 protocol: increases the capacity of the control channel to ten times analog capacity; provides new applications such as private network service; provides a short message service; and reduces power consumption of portable cellular telephones by supporting paging of the portable telephones to prompt them out of an idle mode.
Portable cellular telephones in a conventional IS-136 TDMA system transmit and receive the digital control channel and all the digital traffic channels. The digital control channel is presently used for set-up and monitoring functions, but often has available unused or minimally-used communications capacity.
Messaging service is becoming increasingly commercially important. For messaging service to be successful there should be minimal missed messages, such as from fading. The messaging service must be close to one-hundred percent reliable. To accomplish messaging within a local area, retransmission of the broadcast messaging signals, within a local subportion of a cell, may improve reliability. (The subportion of the cell may be referred to as a micro/picocell). However, use of normal IS-136, infrastructure to rebroadcast the messaging signal within the micro/picocell would result in significant expense and complexity.